Cavity-enhanced resonant photoacoustic spectroscopy with optical feedback cw diode lasers: A novel technique for ultratrace gas analysis and high-resolution spectroscopy J. Chem. Phys. 133, 044308 (2010) Electromechanical probing of ionic currents in energy storage materials Appl. Phys. Lett. 96, 222906 (2010) Broadening effects and ergodicity in deep level photothermal spectroscopy of defect states in semi-insulating GaAs: A combined temperature-, pulse-rate-, and time-domain study of defect state kinetics J. Appl. Phys. 105, 103712 (2009) Measurement of the redistribution of arsenic at nickel silicide/silicon interface by secondary ion mass spectrometry: artifact and optimized analysis conditions J. Appl. Phys. 104, 024313 (2008) Standoff photoacoustic spectroscopy Appl. Phys. Lett. 92, 234102 (2008) Additional information on Rev. Sci. Instrum.The application of different types of acoustic resonators such as pipes, cylinders, and spheres in photoacoustics is considered. This includes a discussion of the fundamental properties of these resonant cavities. Modulated and pulsed laser excitation of acoustic modes is discussed. The theoretical and practical aspects of high-Q and low-Q resonators and their integration into complete photoacoustic detection systems for trace gas monitoring and metrology are covered in detail. The characteristics of the available laser sources and the performance of the photoacoustic resonators, such as signal amplification, are discussed. Setup properties and noise features are considered in detail. This review is intended to give newcomers the information needed to design and construct state-of-the-art photoacoustic detectors for specific purposes such as trace gas analysis, spectroscopy, and metrology.

Nanocrystalline columnar-structured diamond films with column diameters less than 100 nm and thicknesses in the range of 1-5 m were grown on silicon substrates by chemical vapor deposition ͑CVD͒ in a microwave plasma reactor with purified methane and hydrogen used as the reactants. Uniform conformal nucleation densities in excess of 10 12 cm Ϫ2 were accomplished prior to growth by seeding with explosively formed nanodiamonds, which resulted in good optical quality films. The film thickness was measured in situ by the laser reflectometry method. The grain size and optical quality of the films were characterized by scanning electron microscopy and Raman measurements. Broadband surface acoustic wave pulses were used to measure the anomalous dispersion in the layered systems. The experimental dispersion curves were fitted by theory, assuming the diamond film as an isotropic layer on an anisotropic silicon substrate, to determine mean values of the density and Young's modulus of the diamond films. The density was close to the density of single crystal diamond or polycrystalline diamond plates grown by the CVD technique, whereas the Young's modulus varied strongly with the nucleation density between 517 and 1120 GPa. Young's moduli close to the single crystal values were obtained for films grown with a nucleation density у10 12 cm Ϫ2. The thermal diffusivity in these films was measured by the traveling wave technique. The value for ϳ3.5-m-thick nanocrystalline diamond films with nucleation densities у10 12 cm Ϫ2 was ϳ7.2 cm 2 /s, whereas those with lower nucleation densities showed a value of ϳ5.5 cm 2 /s.

A noncontact all-optical method for surface photoacoustics is described. The surface acoustic waves (SAWs) were excited employing a KrF laser and detected with a Michelson interferometer using a 633-nm HeNe laser. Due to an active stabilization scheme developed for the interferometer a surface displacement of 0.2 Å could be detected. The materials investigated included pure materials such as polycrystalline aluminum, and crystalline silicon; films of gold, silver, aluminum, iron, and nickel on fused silica; and a-Si:H on Si(100). In the case of pure materials the shape of the acoustic pulse and the phase velocity were determined. The dispersion of the SAW phase velocity observed for the film systems was used to extract information on the film thickness, density, and transverse and longitudinal sound velocity. Models for the theoretical treatment of film systems and the calculation of dispersion curves are presented.

The Young’s modulus and Poisson’s ratio of high-quality silicon nitride films with 800 nm thickness, grown on silicon substrates by low-pressure chemical vapor deposition, were determined by measuring the dispersion of laser-induced surface acoustic waves. The Young’s modulus was also measured by mechanical tuning of commercially available silicon nitride cantilevers, manufactured from the same material, using the tapping mode of a scanning force microscope. For this experiment, an expression for the oscillation frequencies of two-media beam systems is derived. Both methods yield a Young’s modulus of 280–290 GPa for amorphous silicon nitride, which is substantially higher than previously reported (E=146 GPa). For Poisson’s ratio, a value of ν=0.20 was obtained. These values are relevant for the determination of the spring constant of the cantilever and the effective tip–sample stiffness.

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Laser-generated surface waves provide new tools for studying material properties, from linear elastic behavior to fracture.

Infrared (IR) laser-induced resonant desorption/ablation of benzene layers condensed on liquid-nitrogen-cooled substrates has been investigated using the time-of-flight (TOF) technique. Adsorbates of up to 5 μm thickness were irradiated with a line-tuned TEA CO2 laser. Time-resolved detection of desorbed particles was performed with a quadrupole mass spectrometer (QMS). Measured TOF spectra can usually be well fitted with a stream-modified Maxwell–Boltzmann distribution. Systematic deviations from these fits were observed depending on film thickness, laser fluence, and angle of detection. Spectroscopic data of the adsorbate–substrate system needed for model calculations were measured in situ. The absorption coefficients were found to be fluence dependent. Measurements of the desorption yield and kinetic energy of the desorbed particles were performed with the P932 and P934-CO2 laser lines as a function of film thickness and laser fluence. The solid–liquid phase transition could clearly be observed in these experiments. Average kinetic energies of up to 0.8 eV were measured in the TOF spectra, where the adsorbate temperature could be estimated to be less than 600 K. IR multilayer laser-induced desorption (LID) exhibits features very similar to those reported for UV multilayer LID. A mechanism based on the sudden rise of the adsorbate vapor pressure due to fast energy deposition by the laser pulse is discussed.